Attackers are able to enumerate all devices and computers within a compromised substation network... more Attackers are able to enumerate all devices and computers within a compromised substation network. Digital relays deployed in the substation are the devices with IP addresses that can be discovered in the process of trial-and-error search. This paper is concerned with studies of cyberattacks manipulating digital relays to disruptively disconnect the associated breakers. The plausible enumeration of such disruptive attack for each relay in a substation is verified with the dynamic simulation studies with the special protection system for frequency, voltage, and rotor angle stability. A pertinent approach with smaller scale contingency analysis results is proposed to reduce the enormous computation burden. The devised enumeration reduction method is evaluated using IEEE test cases. The proposed method provides an extensive enumeration strategy that can be used by utility engineers to identify the pivotal relays in the system and can be further strengthened with security protection.
The grid reinforcement, advanced grid stabilizing systems, and inverter-interfaced loads have var... more The grid reinforcement, advanced grid stabilizing systems, and inverter-interfaced loads have varied power system dynamics. The changing trends of various dynamic phenomena need to be scrutinized to ensure future grid reliability. A dynamic behavior-based event signature library of phasor measurement unit (PMU) data has great potential to discover new and unprecedented event signatures. This paper presents an event signature library design that further defines more granular event categories within the major event categories (e.g., frequency, voltage, and oscillation events) provided by electric utilities and regional transmission organizations. The proposed library design embraces a supervised machine learning approach with a deep neural network (DNN) model and manually-generated labels. The input of the model uses representative PMUs that evidently express dominant event signatures. The performance of the event categorization module was evaluated, via information entropy, against labels generated automatically from clustering analyses. We applied the event signature library design to two years of over 1000 actual events in the bulk U.S. power system. The module obtains remarkable event discrimination capability.
We have developed the Reliability Analysis System for Protective Relays (RASPR), which is compose... more We have developed the Reliability Analysis System for Protective Relays (RASPR), which is composed of a database for protective relay equipment and its failures, and reliability analysis part. The data for relay systems and their failures have been collected since fiscal 1997. In this paper, the following suggestions were made from the analysis of the reliability for protective relays: (1) Omission of interruption of automatic checking at fault does not exert an influence on the reliability such as the availability. (2) Improvement of the availability was cleared from the analysis of effect of shortening of the testing time required. (3) The extension of the periodic testing period could be possible if 70% of failures discovered in a periodic testing were detected by continuous monitoring.
High short-circuit current and voltage excursion are two major great concerns for an electricity ... more High short-circuit current and voltage excursion are two major great concerns for an electricity provider in Indonesia, named PLN. These two problems are mainly remarkable in Jakarta area, i.e., the central load of Jawa Bali system. In order to achieve both decrease in the short-circuit current and increase in the voltage level, Insertion of the intermediate 275 kV networks together with the change in the 150 kV networks from loop structure to radial structure is examined with several scenarios. Genetic Algorithm multi-objective optimization technique is also applied for selecting the 275/150 kV transformer reactance in terms of the aforementioned two requirements. The performance of each scenario is verified using the short circuit index, the voltage index and the number of installed 275 kV transmission lines and transformers. Three subsystems in Jakarta area which are Bekasi, Gandul and Kembangan are selected, because these subsystems include most of the issues related to the short-circuit current and the voltage level. The selected scenario successfully reduces the short-circuit currents and increases the voltage level in 150 kV system.
The first-ever Ukraine cyberattack on power grid has proven its devastation by hacking into their... more The first-ever Ukraine cyberattack on power grid has proven its devastation by hacking into their critical cyber assets. With administrative privileges accessing substation networks/local control centers, one intelligent way of coordinated cyberattacks is to execute a series of disruptive switching executions on multiple substations using compromised supervisory control and data acquisition (SCADA) systems. These actions can cause significant impacts to an interconnected power grid. Unlike the previous power blackouts, such high-impact initiating events can aggravate operating conditions, initiating instability that may lead to system-wide cascading failure. A systemic evaluation of "nightmare" scenarios is highly desirable for asset owners to manage and prioritize the maintenance and investment in protecting their cyberinfrastructure. This survey paper is a conceptual expansion of real-time monitoring, anomaly detection, impact analyses, and mitigation (RAIM) framework that emphasizes on the resulting impacts, both on steady-state and dynamic aspects of power system stability. Hypothetically, we associate the combinatorial analyses of steady state on substations/components outages and dynamics of the sequential switching orders as part of the permutation. The expanded framework includes (1) critical/noncritical combination verification, (2) cascade confirmation, and (3) combination re-evaluation. This paper ends with a discussion of the open issues for metrics and future design pertaining the impact quantification of cyber-related contingencies.
This dissertation has been approved in partial fulfillment of the requirements for the Degree of ... more This dissertation has been approved in partial fulfillment of the requirements for the Degree of DOCTOR OF PHILOSOPHY in Electrical Engineering.
This paper presents the recent activities of the Joint Working Group CIGRE C4/C6.35/CIRED. Specif... more This paper presents the recent activities of the Joint Working Group CIGRE C4/C6.35/CIRED. Specifically, the characteristics of Inverter Based Generation (IBG) is compared in detail with the characteristics of synchronous generators used in conventional power plants. In this context, the main differences are identified as: 1) the inertia; 2) the fault current provision; 3) the synchronization capability; and 4) the fixed internal voltage source. Those characteristics are provided by synchronous generators, but they are not easily provided by IBG. In order to overcome these differences grid code requirements for IBG need to be updated and thus, IBG units also have to provide ancillary services. Moreover, the paper presents the characteristics of IBG from the protection point of view. The internal and external protection of IBG is described in detail and examples are given.
The lack of sufficient labeled events and long training time limit the applicability of deep neur... more The lack of sufficient labeled events and long training time limit the applicability of deep neural network-based power system event identification using synchrophasor data. In this paper, we propose to leverage transfer learning technique to boost the reliability and reduce the required training time of neural classifier for power system event identification. We use the weights of a neural classifier trained on one transmission system as the initial parameters of another neural classifier for a different transmission system. Numerical tests with real-world synchrophasor data from the Eastern and Western Interconnections of the United States show that the proposed transfer learning approach is very effective in not only improving the training reliability but also reducing the training time.
25 Abstract The increasing penetration of Inverter Based Generation (IBG) over the last years has... more 25 Abstract The increasing penetration of Inverter Based Generation (IBG) over the last years has led to much effort on the development of IBG models for power system dynamic studies. CIGRE and CIRED established the joint working group CIGRE C4/C6.35/CIRED: “Modelling and dynamic performance of inverter based generation in power system transmission and distribution studies” with the aim of collecting the present best practices in the industry on modelling of IBG for power system dynamic studies, with the focus on photovoltaic systems. For that purpose, a questionnaire was distributed to utilities and system operators around the world. This paper summarizes some of the key findings about: 1) the studied power system; 2) the used IBG models (RMS and EMT models); and 3) the type of the performed studies. This survey supports utilities and system operators as well as research institutes and academia to benchmark their approach against the prevailing international industry practice.
2019 IEEE Sustainable Power and Energy Conference (iSPEC), 2019
An increasing number of phasor measurement units (PMUs) are being installed to improve power syst... more An increasing number of phasor measurement units (PMUs) are being installed to improve power systems' reliability and visibility throughout the world. Due to the high sampling speed, PMUs generate a large volume of streaming synchrophasor data. This huge dataset calls for robust and efficient data analytic tools to discover and label system events, which will greatly enhance the stability of power systems. In this work, we introduce a novel event discovery and labeling framework based on matrix profile. This framework is model-free, fast, scalable, and only requires one user-defined parameter. Since matrix profiles are built by measuring the similarities between subsequences of a time series, our approach has great potential in automatically labeling the system events in the synchrophasor data. Case studies are carried out on real-world PMU data to validate the effectiveness of the proposed framework.
Electric vehicles (EV) and photovoltaic (PV) generation are widely recognized around the world. M... more Electric vehicles (EV) and photovoltaic (PV) generation are widely recognized around the world. Most EV owners in the major Chinese cities are forced to charge their EV batteries at the workplace during the daytime due to the limited space near their homes, which will increase the peak load during the daytime. On the other hand, the PV output is most likely to have a peak at around noon, which means, PVs could have a potential capability to compensate the EV charging load. An EV owner-friendly charging strategy based on PV utilization which alleviates both the EV charging constraints and the negative impact of the EV charging load on the grid is proposed. The PV utilization for compensating the unconstrained EV charging load is maximized to derive the maximum number of EVs with unconstrained charging. If the actual number of EVs exceeds the maximum number, a portion of EVs have to be charged only from the grid. Then, the line loss is introduced as the optimization objective in which the charging states are regulated. The case study shows that the proposed strategy can successfully increase the number of EVs with unconstrained charging, and reduce the peak-to-peak of the load curve.
IEEE Power and Energy Technology Systems Journal, 2018
Dynamic simulations have played an important role in assessing the power system dynamic studies. ... more Dynamic simulations have played an important role in assessing the power system dynamic studies. The appropriate numerical model is the key to obtain correct dynamic simulation results. In addition, the appropriate model including the selection of the individual model component (such as protections, controls, and capabilities) is different depending on the type of phenomena to be observed or examined. However, the proper selection of the model is not an easy task, especially for inverter-based generators (IBGs). Considerable industry experience concerning power system dynamic studies and the dynamics of the IBGs is required for the proper selection of the IBG model. The established CIGRE C4/C6.35/CIRED joint working group (JWG) has gathered a wide variety of experts, which fully cover the required industry experience. The JWG provides the guidance on the model selection for analyzing the phenomena, such as frequency deviation, large voltage deviation, and long-term voltage deviation, individually. This helps to reduce the computational burden, as well as it clarifies the required characteristics/functions that should be represented for the power system dynamic studies with the IBGs.
Owing to the increasing penetration level of Inverter Based Generation (IBG) over the last years,... more Owing to the increasing penetration level of Inverter Based Generation (IBG) over the last years, there has been much effort on the development of IBG models for power system dynamic studies. Therefore, CIGRE and CIRED have established a joint working group CIGRE C4/C6.35/CIRED: 'Modelling and dynamic performance of inverter based generation in power system transmission and distribution studies' with the aim of collecting the present best practices in the industry on modelling of IBG for power system dynamic studies, with the focus on PhotoVoltaic (PV) systems. For this purpose, a questionnaire was developed and distributed to utilities and system operators around the world. This paper summarises some of the key findings and observations and identifies prevalent information about: (i) the type of IBG technology that is modelled (e.g. wind, PV etc.); (ii) the used IBG models (individual or aggregated models); and (iii) the type of the power system dynamic study performed. This survey supports utilities and system operators as well as research institutes and academia to benchmark their approach against the prevailing international industry practice.
2012 10th International Power & Energy Conference (IPEC), 2012
Inappropriate load models could cause discrepancies between the measured and simulated responses ... more Inappropriate load models could cause discrepancies between the measured and simulated responses in both the steady-state and transient state. Therefore, more accurate load models and their parameters need to be derived with the aid of measured data. Although more sophisticated measurement devices have been developed, the whole measured data such as for 30 seconds should not be used for deriving load model parameters, because the natural change in load structures regardless of voltage- and frequency-dependent load can deteriorate the accuracy of the derived voltage- and frequency-dependent load model parameters. In order to extract measured data that do not include the natural change in load structure, an automatic extraction method suitable for deriving load model parameters using a Fuzzy Inference System (FIS) is developed. The suitable data length can be specified using the correlation index between active power load and load bus voltage provided by the FIS. The measured data which are not used for the learning algorithm are used to validate the performance of the developed method.
International Journal of Smart Grid and Clean Energy, 2013
The participation of power electronics interfaced loads or inverter-based loads has increased ste... more The participation of power electronics interfaced loads or inverter-based loads has increased steadily over the last few decades and is expected to continue to increase. Such participation reduces the effect of loads on mitigating voltage and frequency variations, which is also called the self-regulation characteristic of loads. In order to restore the decreasing self-regulation characteristic of loads, an autonomous load-reduction control scheme which reduces electric loads by sending onset signals at 49.2 Hz was developed. The developed scheme reduces the active power consumption by 5% for 10 minutes. After the frequency recovers at over 49.2 Hz, the scheme allows the active power consumption to return to the pre-control level. The major benefits of the scheme are almost no extra cost of implementation and almost no inconvenience for appliance owners. Therefore, loads with this scheme are expected to be classified in the smart load category in the future. The autonomous load-reduction control scheme was implemented in a residential air-conditioner made by a major manufacturer and performed as expected.
Integrating wind power generation into small islands has been one of the demonstration projects i... more Integrating wind power generation into small islands has been one of the demonstration projects in Okinawa Prefecture, Japan. Since such integration could deteriorate power quality, including frequency, in an island grid, a frequency-stabilizing system using flywheels has been integrated into a small island. In order to establish a proper frequency-stabilizing scheme for a small island, an accurate model of a diesel generator including a governor is vital. Therefore, a model was developed through generator dump tests. A new frequency-stabilizing scheme was also developed through the time-domain simulation of the island grid model, which consists of the above mentioned diesel generator model and negative load change representing wind power variation. The developed stabilizing scheme was applied to the flywheels in the island grid and revealed great performance for mitigating frequency variation.
IEEE Open Access Journal of Power and Energy, 2020
The feed-in tariff, introduced in 2012, led to a significant increase in Photovoltaics (PVs) thro... more The feed-in tariff, introduced in 2012, led to a significant increase in Photovoltaics (PVs) throughout Japan. About half of PVs are three-phase PVs that are connected to low voltage or medium voltage networks. Central Research Institute of Electric Power Industry (CRIEPI) has developed root-mean square-based time-domain power system analysis tools used by all the Japanese utilities for dynamic studies following balanced and unbalanced faults for over the last thirty years. Two 10 kW three-phase PV inverter were tested in the CRIEPI's test lab reproducing various levels of the voltage dips that come from threephase balanced and unbalanced faults with various fault duration. The PV model was developed and validated, comparing measured responses obtained in the test lab with simulated responses obtained by the time-domain simulation tool. Sensitivities of identified parameters to the model error are carefully examined, which proves that the same model parameters may be used for balanced and unbalanced faults. Derived model parameters are further verified, comparing the simulated response of the combined two PV outputs with the measured response. The excellent match of those responses demonstrates that individually identified parameters for the two single PV inverters are also adequate for representing the combined PV dynamics. INDEX TERMS Inverters, laboratory test, modeling, photovoltaics, power system, RMS model, three-phase inverter, unbalanced fault.
Attackers are able to enumerate all devices and computers within a compromised substation network... more Attackers are able to enumerate all devices and computers within a compromised substation network. Digital relays deployed in the substation are the devices with IP addresses that can be discovered in the process of trial-and-error search. This paper is concerned with studies of cyberattacks manipulating digital relays to disruptively disconnect the associated breakers. The plausible enumeration of such disruptive attack for each relay in a substation is verified with the dynamic simulation studies with the special protection system for frequency, voltage, and rotor angle stability. A pertinent approach with smaller scale contingency analysis results is proposed to reduce the enormous computation burden. The devised enumeration reduction method is evaluated using IEEE test cases. The proposed method provides an extensive enumeration strategy that can be used by utility engineers to identify the pivotal relays in the system and can be further strengthened with security protection.
The grid reinforcement, advanced grid stabilizing systems, and inverter-interfaced loads have var... more The grid reinforcement, advanced grid stabilizing systems, and inverter-interfaced loads have varied power system dynamics. The changing trends of various dynamic phenomena need to be scrutinized to ensure future grid reliability. A dynamic behavior-based event signature library of phasor measurement unit (PMU) data has great potential to discover new and unprecedented event signatures. This paper presents an event signature library design that further defines more granular event categories within the major event categories (e.g., frequency, voltage, and oscillation events) provided by electric utilities and regional transmission organizations. The proposed library design embraces a supervised machine learning approach with a deep neural network (DNN) model and manually-generated labels. The input of the model uses representative PMUs that evidently express dominant event signatures. The performance of the event categorization module was evaluated, via information entropy, against labels generated automatically from clustering analyses. We applied the event signature library design to two years of over 1000 actual events in the bulk U.S. power system. The module obtains remarkable event discrimination capability.
We have developed the Reliability Analysis System for Protective Relays (RASPR), which is compose... more We have developed the Reliability Analysis System for Protective Relays (RASPR), which is composed of a database for protective relay equipment and its failures, and reliability analysis part. The data for relay systems and their failures have been collected since fiscal 1997. In this paper, the following suggestions were made from the analysis of the reliability for protective relays: (1) Omission of interruption of automatic checking at fault does not exert an influence on the reliability such as the availability. (2) Improvement of the availability was cleared from the analysis of effect of shortening of the testing time required. (3) The extension of the periodic testing period could be possible if 70% of failures discovered in a periodic testing were detected by continuous monitoring.
High short-circuit current and voltage excursion are two major great concerns for an electricity ... more High short-circuit current and voltage excursion are two major great concerns for an electricity provider in Indonesia, named PLN. These two problems are mainly remarkable in Jakarta area, i.e., the central load of Jawa Bali system. In order to achieve both decrease in the short-circuit current and increase in the voltage level, Insertion of the intermediate 275 kV networks together with the change in the 150 kV networks from loop structure to radial structure is examined with several scenarios. Genetic Algorithm multi-objective optimization technique is also applied for selecting the 275/150 kV transformer reactance in terms of the aforementioned two requirements. The performance of each scenario is verified using the short circuit index, the voltage index and the number of installed 275 kV transmission lines and transformers. Three subsystems in Jakarta area which are Bekasi, Gandul and Kembangan are selected, because these subsystems include most of the issues related to the short-circuit current and the voltage level. The selected scenario successfully reduces the short-circuit currents and increases the voltage level in 150 kV system.
The first-ever Ukraine cyberattack on power grid has proven its devastation by hacking into their... more The first-ever Ukraine cyberattack on power grid has proven its devastation by hacking into their critical cyber assets. With administrative privileges accessing substation networks/local control centers, one intelligent way of coordinated cyberattacks is to execute a series of disruptive switching executions on multiple substations using compromised supervisory control and data acquisition (SCADA) systems. These actions can cause significant impacts to an interconnected power grid. Unlike the previous power blackouts, such high-impact initiating events can aggravate operating conditions, initiating instability that may lead to system-wide cascading failure. A systemic evaluation of "nightmare" scenarios is highly desirable for asset owners to manage and prioritize the maintenance and investment in protecting their cyberinfrastructure. This survey paper is a conceptual expansion of real-time monitoring, anomaly detection, impact analyses, and mitigation (RAIM) framework that emphasizes on the resulting impacts, both on steady-state and dynamic aspects of power system stability. Hypothetically, we associate the combinatorial analyses of steady state on substations/components outages and dynamics of the sequential switching orders as part of the permutation. The expanded framework includes (1) critical/noncritical combination verification, (2) cascade confirmation, and (3) combination re-evaluation. This paper ends with a discussion of the open issues for metrics and future design pertaining the impact quantification of cyber-related contingencies.
This dissertation has been approved in partial fulfillment of the requirements for the Degree of ... more This dissertation has been approved in partial fulfillment of the requirements for the Degree of DOCTOR OF PHILOSOPHY in Electrical Engineering.
This paper presents the recent activities of the Joint Working Group CIGRE C4/C6.35/CIRED. Specif... more This paper presents the recent activities of the Joint Working Group CIGRE C4/C6.35/CIRED. Specifically, the characteristics of Inverter Based Generation (IBG) is compared in detail with the characteristics of synchronous generators used in conventional power plants. In this context, the main differences are identified as: 1) the inertia; 2) the fault current provision; 3) the synchronization capability; and 4) the fixed internal voltage source. Those characteristics are provided by synchronous generators, but they are not easily provided by IBG. In order to overcome these differences grid code requirements for IBG need to be updated and thus, IBG units also have to provide ancillary services. Moreover, the paper presents the characteristics of IBG from the protection point of view. The internal and external protection of IBG is described in detail and examples are given.
The lack of sufficient labeled events and long training time limit the applicability of deep neur... more The lack of sufficient labeled events and long training time limit the applicability of deep neural network-based power system event identification using synchrophasor data. In this paper, we propose to leverage transfer learning technique to boost the reliability and reduce the required training time of neural classifier for power system event identification. We use the weights of a neural classifier trained on one transmission system as the initial parameters of another neural classifier for a different transmission system. Numerical tests with real-world synchrophasor data from the Eastern and Western Interconnections of the United States show that the proposed transfer learning approach is very effective in not only improving the training reliability but also reducing the training time.
25 Abstract The increasing penetration of Inverter Based Generation (IBG) over the last years has... more 25 Abstract The increasing penetration of Inverter Based Generation (IBG) over the last years has led to much effort on the development of IBG models for power system dynamic studies. CIGRE and CIRED established the joint working group CIGRE C4/C6.35/CIRED: “Modelling and dynamic performance of inverter based generation in power system transmission and distribution studies” with the aim of collecting the present best practices in the industry on modelling of IBG for power system dynamic studies, with the focus on photovoltaic systems. For that purpose, a questionnaire was distributed to utilities and system operators around the world. This paper summarizes some of the key findings about: 1) the studied power system; 2) the used IBG models (RMS and EMT models); and 3) the type of the performed studies. This survey supports utilities and system operators as well as research institutes and academia to benchmark their approach against the prevailing international industry practice.
2019 IEEE Sustainable Power and Energy Conference (iSPEC), 2019
An increasing number of phasor measurement units (PMUs) are being installed to improve power syst... more An increasing number of phasor measurement units (PMUs) are being installed to improve power systems' reliability and visibility throughout the world. Due to the high sampling speed, PMUs generate a large volume of streaming synchrophasor data. This huge dataset calls for robust and efficient data analytic tools to discover and label system events, which will greatly enhance the stability of power systems. In this work, we introduce a novel event discovery and labeling framework based on matrix profile. This framework is model-free, fast, scalable, and only requires one user-defined parameter. Since matrix profiles are built by measuring the similarities between subsequences of a time series, our approach has great potential in automatically labeling the system events in the synchrophasor data. Case studies are carried out on real-world PMU data to validate the effectiveness of the proposed framework.
Electric vehicles (EV) and photovoltaic (PV) generation are widely recognized around the world. M... more Electric vehicles (EV) and photovoltaic (PV) generation are widely recognized around the world. Most EV owners in the major Chinese cities are forced to charge their EV batteries at the workplace during the daytime due to the limited space near their homes, which will increase the peak load during the daytime. On the other hand, the PV output is most likely to have a peak at around noon, which means, PVs could have a potential capability to compensate the EV charging load. An EV owner-friendly charging strategy based on PV utilization which alleviates both the EV charging constraints and the negative impact of the EV charging load on the grid is proposed. The PV utilization for compensating the unconstrained EV charging load is maximized to derive the maximum number of EVs with unconstrained charging. If the actual number of EVs exceeds the maximum number, a portion of EVs have to be charged only from the grid. Then, the line loss is introduced as the optimization objective in which the charging states are regulated. The case study shows that the proposed strategy can successfully increase the number of EVs with unconstrained charging, and reduce the peak-to-peak of the load curve.
IEEE Power and Energy Technology Systems Journal, 2018
Dynamic simulations have played an important role in assessing the power system dynamic studies. ... more Dynamic simulations have played an important role in assessing the power system dynamic studies. The appropriate numerical model is the key to obtain correct dynamic simulation results. In addition, the appropriate model including the selection of the individual model component (such as protections, controls, and capabilities) is different depending on the type of phenomena to be observed or examined. However, the proper selection of the model is not an easy task, especially for inverter-based generators (IBGs). Considerable industry experience concerning power system dynamic studies and the dynamics of the IBGs is required for the proper selection of the IBG model. The established CIGRE C4/C6.35/CIRED joint working group (JWG) has gathered a wide variety of experts, which fully cover the required industry experience. The JWG provides the guidance on the model selection for analyzing the phenomena, such as frequency deviation, large voltage deviation, and long-term voltage deviation, individually. This helps to reduce the computational burden, as well as it clarifies the required characteristics/functions that should be represented for the power system dynamic studies with the IBGs.
Owing to the increasing penetration level of Inverter Based Generation (IBG) over the last years,... more Owing to the increasing penetration level of Inverter Based Generation (IBG) over the last years, there has been much effort on the development of IBG models for power system dynamic studies. Therefore, CIGRE and CIRED have established a joint working group CIGRE C4/C6.35/CIRED: 'Modelling and dynamic performance of inverter based generation in power system transmission and distribution studies' with the aim of collecting the present best practices in the industry on modelling of IBG for power system dynamic studies, with the focus on PhotoVoltaic (PV) systems. For this purpose, a questionnaire was developed and distributed to utilities and system operators around the world. This paper summarises some of the key findings and observations and identifies prevalent information about: (i) the type of IBG technology that is modelled (e.g. wind, PV etc.); (ii) the used IBG models (individual or aggregated models); and (iii) the type of the power system dynamic study performed. This survey supports utilities and system operators as well as research institutes and academia to benchmark their approach against the prevailing international industry practice.
2012 10th International Power & Energy Conference (IPEC), 2012
Inappropriate load models could cause discrepancies between the measured and simulated responses ... more Inappropriate load models could cause discrepancies between the measured and simulated responses in both the steady-state and transient state. Therefore, more accurate load models and their parameters need to be derived with the aid of measured data. Although more sophisticated measurement devices have been developed, the whole measured data such as for 30 seconds should not be used for deriving load model parameters, because the natural change in load structures regardless of voltage- and frequency-dependent load can deteriorate the accuracy of the derived voltage- and frequency-dependent load model parameters. In order to extract measured data that do not include the natural change in load structure, an automatic extraction method suitable for deriving load model parameters using a Fuzzy Inference System (FIS) is developed. The suitable data length can be specified using the correlation index between active power load and load bus voltage provided by the FIS. The measured data which are not used for the learning algorithm are used to validate the performance of the developed method.
International Journal of Smart Grid and Clean Energy, 2013
The participation of power electronics interfaced loads or inverter-based loads has increased ste... more The participation of power electronics interfaced loads or inverter-based loads has increased steadily over the last few decades and is expected to continue to increase. Such participation reduces the effect of loads on mitigating voltage and frequency variations, which is also called the self-regulation characteristic of loads. In order to restore the decreasing self-regulation characteristic of loads, an autonomous load-reduction control scheme which reduces electric loads by sending onset signals at 49.2 Hz was developed. The developed scheme reduces the active power consumption by 5% for 10 minutes. After the frequency recovers at over 49.2 Hz, the scheme allows the active power consumption to return to the pre-control level. The major benefits of the scheme are almost no extra cost of implementation and almost no inconvenience for appliance owners. Therefore, loads with this scheme are expected to be classified in the smart load category in the future. The autonomous load-reduction control scheme was implemented in a residential air-conditioner made by a major manufacturer and performed as expected.
Integrating wind power generation into small islands has been one of the demonstration projects i... more Integrating wind power generation into small islands has been one of the demonstration projects in Okinawa Prefecture, Japan. Since such integration could deteriorate power quality, including frequency, in an island grid, a frequency-stabilizing system using flywheels has been integrated into a small island. In order to establish a proper frequency-stabilizing scheme for a small island, an accurate model of a diesel generator including a governor is vital. Therefore, a model was developed through generator dump tests. A new frequency-stabilizing scheme was also developed through the time-domain simulation of the island grid model, which consists of the above mentioned diesel generator model and negative load change representing wind power variation. The developed stabilizing scheme was applied to the flywheels in the island grid and revealed great performance for mitigating frequency variation.
IEEE Open Access Journal of Power and Energy, 2020
The feed-in tariff, introduced in 2012, led to a significant increase in Photovoltaics (PVs) thro... more The feed-in tariff, introduced in 2012, led to a significant increase in Photovoltaics (PVs) throughout Japan. About half of PVs are three-phase PVs that are connected to low voltage or medium voltage networks. Central Research Institute of Electric Power Industry (CRIEPI) has developed root-mean square-based time-domain power system analysis tools used by all the Japanese utilities for dynamic studies following balanced and unbalanced faults for over the last thirty years. Two 10 kW three-phase PV inverter were tested in the CRIEPI's test lab reproducing various levels of the voltage dips that come from threephase balanced and unbalanced faults with various fault duration. The PV model was developed and validated, comparing measured responses obtained in the test lab with simulated responses obtained by the time-domain simulation tool. Sensitivities of identified parameters to the model error are carefully examined, which proves that the same model parameters may be used for balanced and unbalanced faults. Derived model parameters are further verified, comparing the simulated response of the combined two PV outputs with the measured response. The excellent match of those responses demonstrates that individually identified parameters for the two single PV inverters are also adequate for representing the combined PV dynamics. INDEX TERMS Inverters, laboratory test, modeling, photovoltaics, power system, RMS model, three-phase inverter, unbalanced fault.
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Papers by Koji Yamashita